Armoured, flexible pipe

ABSTRACT

A flexible, armored pipe is disclosed. In an exemplary embodiment, the flexible, armored pipe includes an impermeable liner, an outer armoring layer, and an inner armoring layer. The inner armoring layer includes one or more wound armoring elements, and the outer armoring layer is placed on the outside of the liner, and includes at least two layers of wound armoring elements which are completely or partly permeable for fluids. Further, the inner armoring layer is placed on the inside of the liner. In certain embodiments, the inner armoring is built up of wound profiles, K profiles, or profiles which include a rolled strip.

This application is a national stage filing under 35 U.S.C. §371 ofInternational Application No. PCT/ DK01/00641, filed on Mar. 10, 2001,which published in the English language. This application also claimsthe benefit of priority under 35 U.S.C.

119(a) to DK Patent Application No. PA-2000-01510, filed on Oct. 10,2000.

The present invention relates to a flexible, armoured pipe comprising atleast an impermeable liner, an outer armouring layer and an innerarmouring layer consisting of one or more wound armouring elements.

Such pipes are used for the transport of oil and gas in deep or varyingdepths of water. These pipes are particularly suitable for the transportof oil from underwater installations to floating installations on thesurface of the sea, where the oil is refined or transported further forprocessing.

For example, JP3265781 and FR2764669-A1 describe armoured flexible pipeswhere the whole of the armouring is surrounded by an impermeable sheathwhich prevents the ingress of fluids from the surroundings to the pipe'sarmouring layer, which provides the advantage that the pipe's armouringcan be executed in materials which, if unprotected, cannot withstand thesurrounding environment.

Conversely, U.S. Pat. No. 4,402,346 describes a pipe where the armouringis surrounded by a permeable outer sheath, which provides the advantagethat aggressive gases, which diffuse out through the inner liner, do notaccumulate in the armouring layer. However, a problem in connection withthis method is that fluids will penetrate through the outer sheath andexercise a hydrostatic pressure corresponding to the pressure of thesurroundings in the armouring layer and herewith on the non-reinforcedliner, the result being that under certain conditions the surroundingpressure will be able to crush or collapse the liner. Moreover, theliner will be able to collapse if a high tensile load is placed on thepipe.

It is the object of the present invention to provide a flexible pipewhere the resistance against crushing and collapse of the liner as aresult of the surrounding pressure is retained, while at the same timethe pipe's outer armouring is protected against the damaging effect offluids which diffuse from the inside of the liner and out to thesurroundings.

The object of the invention is achieved with a pipe of the typedisclosed in the preamble to claim 1, which is characterised in that theouter armouring layer is placed on the outside of the liner and consistsof at least two layers of wound armouring elements which are partly orcompletely permeable for fluids, while the inner armouring layer isplaced on the inside of the liner.

With this construction, a flexible pipe is provided where the innerarmouring layer is in contact with the fluid, which is to be transportedin the pipe, while the outer armouring layer and the outer side of theimpermeable liner are in contact with the surroundings.

This means that the inner armouring layer absorbs the hydrostaticpressure applied to the liner, unlike earlier where this pressure waspartly or completely absorbed by one of two layers of armour placed inbetween the impermeable liner and an outer, impermeable sheath.

Moreover, since no significant restrictions to mass transport existoutside the impermeable liner, gases, which diffuse through the liner,will now be able to escape to the surroundings.

In other words, a flexible pipe with only three layers is now provided,which meets the demands most often placed on flexible pipes with severallayers.

Moreover, the pipe achieved is one where the different layers are usedmore effectively than has hitherto been the case, which, if the pipeproduced is long, affords a saving in weight, which is of greatimportance.

The forces, which the inner armouring is required to withstand, dependon the use of the pipe. If, for example, the pipe is used as productionpipe between a floating installation on the surface of the sea and aninstallation on the seabed, the inner armouring in the pipe's lower partis loaded primarily as a result of hydrostatic forces stemming from thatwater pressure which acts on the outside of the liner. In contrasthereto, the inner armouring in the pipe's upper part will be loadedprimarily as a result of the forces with which the outer armouringclamps around the liner due to the axial load which is applied to theouter armouring.

Since the outer armouring lies around the pipe's impermeable liner, thisarmouring will not be required to absorb forces resulting from the outerhydrostatic pressure. The outer armouring in the pipe's lower part shallthus primarily absorb the forces which act on the liner as a result ofthe pipe's inner over-pressure, while the outer armouring in the top ofthe pipe shall be able to absorb the forces not only from the pipe'sinner over-pressure, but also from the axial forces which stem from theinherent weight of the pipe. Since a considerable part of the outerarmouring is wound with an angle different from zero, relative to theaxis of the pipe, the absorption of axial forces will give rise to aquasi-hydrostatic pressure on the liner, which must be absorbed by theinner armouring. Moreover, a part of or the whole of the outer armouringwill be wound with an angle which ensures that the outer armouring cancounteract deformation of the liner as a result of the pressure on theinside of the liner.

In that the outer pressure influences the outer armouring layershydrostatically, and in that the outer pressure acts directly on thepipe's liner, it is not decisive for the function of the pipe that theouter armouring layer possesses compressive rigidity in directionsparallel with the surface of the pipe.

Finally it should be noted that the outer armouring layer gives theliner resistance against increase of the volume surrounded by the liner.The liner will attempt to expand its volume, either as a result of theinner pressure in the pipe, or as a result of tensile forces in thelongitudinal direction of the liner.

On the outside of the liner, but under the outer armouring layer, one ormore layers can be provided which are without structural significancebut which give the liner additional thermal resistance, so that theexchange of thermal energy between the fluid transported in the linerand the liner's surroundings is reduced.

With the object of protecting the outer armour against mechanicaldamages, a permeable sheath can lie on the outside of the outerarmouring layer.

It must be added that the different layers (liner and inner/outerarmouring layers) are not chemically bound to one another, which ensuresthe flexibility of the pipe. Since the individual elements of the pipeare not chemically bound to one another, this type of pipe is referredto in the literature as “unbonded”.

Expedient embodiments of the inner armouring layer are disclosed in moredetail in the claims 2–7 , while expedient embodiments of the outerarmouring layer are disclosed in more detail in the claims 8–12.

The invention will now be explained in more detail with reference to thedrawing, in which:

FIG. 1 schematically shows the customary structure of a known pipe,

FIG. 2 schematically shows an embodiment of a pipe according to theinvention,

FIG. 3 shows a K-profile for the inner armor according to the invention,and

FIG. 4 shows a further embodiment corresponding to FIG. 3.

The reference number 2 in FIG. 1 indicates a liner, which is surroundedby two or more armouring layers 3,4, which in turn are surrounded by animpermeable outer sheath 5. A more detailed structure of such a pipe canbe found, for example, in WO 00/36324, and therefore this will not bediscussed in more detail here.

It should be noted, however, that the impermeable outer sheath 5 ensuresthat the armouring layers 3,4 are able to relieve the hydrostaticpressure placed on the pipe, in that the armouring layers 3 and 4 have avery great rigidity. The liner 2 is hereby relieved.

An additional advantage of placing the armouring layers between theliner 2 and the outer sheath 5 is that by this construction there isachieved a complete or partial protection of the armouring layers 3,4,which can be produced as wire, against corrosion, which means thatnon-rustproof types of steel can be used as armouring material.

In FIG. 2 it is shown how a pipe according to the invention can be builtup. A liner 2 a surrounds an inner armouring layer 1 a, the object ofwhich is to prevent the collapse of the liner 2 a. In a preferredembodiment, the inner armouring layer 1 a is wound from long profileswith a numerical winding angle of more than 55° relative to the axis ofthe pipe. In a particularly preferred embodiment, these profiles will bemade of rolled stainless steel.

On the outside of the liner 2 a one or more armouring layers 3 a arelaid, where at least two of these are wound with a numerical anglegreater than 45° relative to the axis of the pipe.

In a particularly preferred embodiment, the outer armouring layer 3 isproduced from aramide cord on which a layer of thermoplastic polymer isapplied.

In a second particularly preferred embodiment, the outer armouring layer3 a is completely or partly produced from a carbon-fibre-reinforcedmaterial.

Numerous other armouring materials can, however, be envisaged in theouter armouring layer, merely providing that these meet the demandsregarding strength and resistance to the surrounding environment.

In some cases, consideration can be given to the application of aprotection layer on the outside of the outer armouring layer 3 a. Thisprotection layer, which is permeable for fluids, has only a secondaryfunction and will not be dealt with further.

The invention will now explained more fully in connection with thefollowing examples:

EXAMPLE 1 Pipes for the Transport of Oil Between an Installation on theSeabed and a Floating Installation.

This example describes a “free hanging” configuration, where the depthof the pipe under the surface of the sea is a monotonic increasingfunction of the length. In this configuration, the hydrostatic pressurearound the pipe therefore increases monotonically along the length ofthe pipe.

The liner is made of a PVdF, the object of which is to form an effectivediffusion barrier between the fluid, which is transported in the pipe,and the surrounding environment. In order to prevent an unintentionalcooling of the transported fluid, a layer of polypropylene is extrudedon the outside of the liner, the purpose of which is to serve as athermal barrier. Although polypropylene is given here as an example,other materials and material combinations can just as well be used.Especially material combinations that include syntactic foam as acomponent can be considered to be suitable in this application.

In order to arm the liner against volume reduction, the inside of theliner is armed with a 12 mm-thick armouring layer, which is wound up ofK profiles produced from duplex steel. The advantage of making use of Kprofiles in particular is that these display an especially greatresistance against crushing as a result of the influences of outerpressure.

The outer armouring is built up of thin tapes of a carbon/epoxycomposite, in between which a thermoplastic is melted. The outerarmouring is wound on with an angle of approx. +/−55° in relation to thelongitudinal axis of the pipe.

In order to protect the outer armouring during laying-out and operation,a sleeve of aramide is woven out over the outer armouring. This aramidesleeve gives the pipe a great abrasive strength. At the same time, thissleeve is so open to mass transport that a free or almost free transportof fluids can take place through the sleeve. Since said aramide sleeveis exposed to sunlight, a further covering layer will be applied in thezone close to the surface of the sea in order to prevent decompositionas a result of UV radiation. Said sleeve is woven in such a manner thatit is resilient in the event of the pipe being compressed. In this way,in the event of the pipe being exposed to compression in the axialdirection, it is ensured that the pipe's tensile armour can migrateradially and herewith reduce the compressive forces in this layer to anacceptable level.

EXAMPLE 2 Pipes for Transport of Oil Between an Installation on theSeabed and a Floating Installation.

This example describes a “steep S” configuration, where the depth of thepipe below the surface of the sea is not a monotonic increasing functionof the length. In this configuration, the hydrostatic pressure aroundthe pipe is therefore not monotonically increasing along the length ofthe pipe. The design presented here will be suitable for use in waters2000 meters deep.

The liner is made of a PVdF, the object of which is to form an effectivediffusion barrier between the fluid transported in the pipe and thesurrounding environment. In order to prevent an unintentional cooling ofthe transported fluid, a layer of polypropylene is extruded on theoutside of the liner, the object of which is to serve as thermalbarrier.

In order to arm the liner against volume reduction, the inside of theliner is armed with a 12 mm-thick armouring layer wound up of K profilesproduced from duplex steel (as shown for example in FIGS. 3 and 4.)

The advantage of making use of K profiles in particular is that thesedisplay especially great resistance against crushing as a result of theinfluences of outer pressure.

The outer armouring is built up of two layers, the first of whichconsists of 2N layer of aramide cord, around which a layer of polymer isextruded. This first layer is wound with an angle of about 55° inrelation to the axis of the pipe, and is the primary, force-bearinglayer. Here, N denotes a whole number. Around this first layer athinner, second layer is wound with a winding angle, which isconsiderably greater than 55° in relation to the axis of the pipe. Theobject of this second layer is to secure the primary, force-bearinglayer in situations where this layer is non-supporting, since the netforces on the pipe result in a compressive clamping situation.

In order to further secure the position of the armouring wires, thearmouring wires are lashed every 5–10 meters, simply to secure theirposition relative to the pipe.

To protect the armouring against damage during the laying-out andoperation, a sheath of polyamide is extruded on the outside of thearmour. In order to ensure that this sheath is permeable, holes with adiameter of approx. 1 centimeter are cut out at intervals of one meter,so that a free exchange of fluids between the inside of the pipe and theannulus of the pipe is ensured. The cutting-out of the holes will alsoensure that the pipe's annulus is filled with seawater, which willensure sufficient cooling of the aramide cords.

It is obvious that the present invention can be exercised in far moreways than disclosed above, in that within the scope of the patent claimsthere is great freedom for application of the principle of theinvention, without this changing the invention's mode of operation.

1. A flexible armored pipe for transporting a fluid substance, theflexible armored pipe comprising an impermeable liner, an outer armoringlayer, and an inner armoring layer consisting of one or more woundarmoring elements, the inner armoring layer being placed on the insideof the liner and the outer armoring layer is placed on the outside ofthe liner and consisting of at least two layers of wound armoringelements which are completely or partly permeable for fluids, whereinthe outer armoring layer and the outer side of the impermeable liner arein contact with the surroundings so that no significant restrictions tomass transport exist outside the impermeable layer.
 2. The pipeaccording to claim 1, wherein the inner armoring is built up of woundprofiles.
 3. The pipe according to claim 1, wherein the inner armoringis built up of K profiles.
 4. The pipe according to claim 1, wherein theinner armoring is built up of profiles, which consist of rolled strip.5. The pipe according to the claim 1, wherein the inner armoringconsists of a plastic deformable material.
 6. The pipe according to theclaim 1, wherein the inner armoring consists of a type of alloyed steel.7. The pipe according to the claim 1, wherein the inner armoringconsists of titanium or an alloy hereof.
 8. The pipe according to theclaim 1, wherein the outer armoring is wound with long elements.
 9. Thepipe according to claim 8, wherein the outer armoring is wholly orpartly reinforced with a composite material containing carbon fiber. 10.The pipe according to claim 9, wherein the outer armoring is wholly orpartly reinforced with a material containing titanium.
 11. The pipeaccording to claim 9, wherein the outer armoring is wound in such amanner that it does not absorb substantial axial stresses applied to thepipe, but instead relaxes by a mechanical displacement of the armoringelements.
 12. The pipe according to claim 8, wherein the outer armoringis wholly or partly reinforced with a material containing aramide fiber.13. The pipe according to claim 1 further comprising at least onethermally insulating layer between the impermeable liner and the outerarmoring layer.
 14. The pipe according to claim 1, wherein the layers ofthe flexible armored pipe are unbounded.
 15. The pipe according to claim1, wherein the outer armoring layer is produced from aramide cord onwhich a layer of thermoplastic polymer is applied.
 16. The pipeaccording to claim 15, wherein the armoring cord of the outer armoringlayer are lashed every 5–10 meters.
 17. The pipe according claim 1,wherein the flexible armored pipe further comprises a resilient sleeveor sheath around the outer armoring layer, the sleeve or sheath beingopen to a free or almost free transport of fluids between marineenvironment and the outer armoring layer.
 18. The pipe according toclaim 17, wherein the sheath is provided with holes with a diameter ofapproximately 1 centimeter at intervals of 1 meter.